A wide variety of cosmetic compositions containing self-tanning agents have been used to increase the pigmentation of the skin. These compositions have been used to create artificial tans, bronzing the skin in a similar fashion to exposure to the sun. Self-tanning agents are believed to generate skin colouration by reacting with amino acids present in the skin to form coloured chromophores, and hence a tan. However, variation in skin amino acid constitution and content between individuals results in wide variation in the colour achieved with a single product. In order to overcome this, it has been suggested to use colour enhancers to even out these differences by supplementing the amino acids naturally present in the skin.
WO 94/04130, WO 94/13258, and WO 94/22419 disclose apparatus and methods for sunless tanning comprising a fluid comprising dihydroxyacetone, and another fluid formulation comprising a colour enhancer comprising respectively, primary amines, secondary polyamines, and amino acids. Whilst these materials work well as colour enhancers, it has been found that they tend to react too quickly with the self tanning agents, thereby not allowing the self-tanning agents to penetrate the cutaneous layer. As a result, the reaction occurs at the surface of the skin, and may consequently wash off the skin.
EP 0,456,545 B1 and EP 0,500,446 B1 disclose a two-component combination for imparting colour to the skin comprising dihydroxyacetone in component (A) and a monohydroxyindole or disubstituted indole derivative respectively, in component (B). Again, these materials do efficiently increase the colour imparted to the skin by such systems, however safety concerns of the use of these materials have prevented their wide-spread use.
It is therefore desirable to provide improved cosmetic compositions for imparting a natural tan to the skin comprising a self-tanning agent and an alternative colour enhancer that reacts with the self-tanning agent to impart an even and durable colour to the skin with limited irritancy or toxicological potential when topically applied.